This invention relates to a surgical trocar for puncturing the body wall of a patient to provide access to a surgical site during endoscopic surgery. More specifically, it relates to a trocar incorporating a universal seal to minimize or prevent leakage of insufflation fluid from the surgical site through the trocar when instruments are inserted through the trocar.
A critical feature of a trocar is the design of the seal which prevents the passage of insufflation fluid through the trocar when instruments of varying sizes are inserted through it. During endoscopic surgery, the abdomen is insufflated with carbon dioxide to provide space between internal organs and bodily tissue during surgical procedures. First, the trocar obturator, which is the puncturing implement of the trocar assembly, is used to puncture the abdominal wall. The trocar obturator is subsequently removed, the abdomen is inflated, and the trocar cannula remains in place to provide access for surgical instruments to the surgical site. The cannula has a housing and a cannula tube extending from the housing. It is the housing which contains the seal. The housing also contains a valve, typically a flapper valve. When an instrument is inserted through the cannula, the instrument is inserted through the seal and causes the flapper valve to swing out of the way. The seal conforms to the outer diameter of the instrument, and therefore prevents the insufflation gas from exiting the body through the housing of the cannula. When the instrument is removed, the flapper valve automatically swings shut to likewise prevent insufflation gas from escaping.
One type of seal for a trocar is a simple gasket fixed to the cannula housing which has a diameter sized for the insertion and withdrawal of instruments of generally fixed diameter. Although simple in construction, it has the disadvantage of not being able to seal against instruments which have a diameter smaller that that for which the seal was sized. Accordingly, a reducer cap with a gasket diameter smaller than that of the housing to accommodate smaller sized instruments has been developed. The cap snaps onto the housing. Therefore, the surgeon can choose between the larger, fixed gasket of the housing or the smaller one on the reducer cap to ensure that an adequate seal around the instrument would be maintained when the instrument is inserted through the cannula. This reducer cap is described in U.S. Pat. No. 5,338,307.
While the reducer cap provides a greater degree of flexibility for inserting instruments with varying diameters through the cannula, it still requires the surgeon to manipulate the cap to provide the proper seal. Accordingly, efforts have been undertaken to develop an improved seal for a trocar.
A description of the first "universal seal" for a trocar is set forth in U.S. Pat. No. 5,395,342. The seal described in the '342 patent has an elastomeric cone with an aperture at its apex. The cone is fitted over a plurality of resilient legs extending from a frame fixed to the cannula housing. When an instrument is inserted through the seal, the instrument contacts the legs and causes them to expand against the elastomeric cone. This expansion facilitates the expansion of the aperture so it will conform to the outer diameter of the instrument. Significantly, the '342 patent provides the first description which inherently recognizes the less than desirable overall performance of seals composed of conventional elastomeric materials, such as silicone. Accordingly, it describes the use of resilient legs to facilitate the expansion of the seal, which is a key factor in the overall performance of the seal.
The recognition of the necessity of the legs to facilitate the expansion of a seal composed of a conventional elastomer manufactured using conventional techniques cannot be overstated. Without the legs, these elastomeric materials will not expand significantly. Therefore, if the aperture of the elastomeric seal is substantially smaller than the outer diameter of the instrument desired to be inserted through the cannula, the material surrounding the aperture may tear when the instrument is inserted. This, of course, is undesirable and may cause significant leakage of insufflation gas through the cannula.
In addition to the inability of conventional elastomers to provide the requisite degree of expansion, these conventional materials may not provide the required degree of tear resistance to prevent tearing of the seal when an instrument with a pointed tip contacts the outer periphery of the seal. This may occur when the surgeon is trying to insert the instrument through the seal aperture, and misguides the tip so that it contacts the outer periphery instead of the centrally located aperture. The lack of tear resistance has led to the development of seal designs to protect the elastomeric seal during instrument insertion. For example, U.S. Pat. No. 5,342,315 describes the use of "protectors" surrounding the elastomeric seal which come into direct contact with the instrument during instrument insertion. The protectors prevent direct contact of the instrument tip with the elastomeric seal, and therefore significantly minimize or prevent the instrument tip from tearing the outer periphery of the seal. Another protector configuration designed to isolate the instrument from the outer periphery of the elastomeric seal is described in U.S. Pat. No. 5,308,336.
Although universal seals for trocars have been developed to provide a seal against instruments of varying diameters, none of these seals is capable of overcoming the substantial deficiencies inherent in the use of conventional elastomeric materials which are suitable for surgical applications. Therefore, these seals have required the use of additional seal components such as resilient legs or protectors to overcome these material deficiencies. Unfortunately, these additional components add cost, manufacturing complexity and reduced reliability to the overall seal design. It would be highly desirable, in view of this ongoing deficiency, to develop a universal seal for a trocar which does not require the use of resilient legs or protectors to compensate for inadequacies of conventional elastomeric materials adapted for surgical applications.